Prime and composite numbers review

CCSS Math: 4.OA.B.4
Review prime and composite numbers, and try some practice problems.

What are prime numbers?

Prime numbers are numbers with exactly 22 factors.
A prime number's only factors are 1\greenD1 and the number itself\purpleD{\text{itself}}.
77 is an example of a prime number. Its only factors are 1\greenD1 and 7\purpleD7. It is not evenly divisible by any other whole numbers.
A factor is a whole number that can divide evenly into another number.
The factors of 8\purpleD8 are: 1,2,4,\blueD{1, 2, 4}, and 8\blueD8.
8÷1=8\purpleD8 \div \blueD1 = 8
8÷2=4\purpleD8 \div \blueD2 = 4
8÷4=2\purple8 \div \blueD4 = 2
8÷8=1\purpleD8 \div \blueD8 = 1
1,2,4,\blueD{1, 2, 4}, and 8\blueD8 all divide evenly into 8\purpleD8.
Want to learn more about prime numbers? Check out this video.

Practice set 1: Identifying prime numbers

Problem 1A
Which of these numbers is prime?
12, 42, 61, 87, 95\large{12,\ 42,\ 61,\ 87,\ 95}
Choose 1 answer:
Choose 1 answer:

Want to try more problems like this? Check out this exercise.

What are composite numbers?

Composite numbers have more than 22 factors. A composite number has factors in addition to 11 and the number itself\text{itself}.
1616 is an example of a composite number. The factors of 1616 are 1,2,4,81, 2, 4, 8 and 16.16. All of these numbers divide into 1616 evenly.
Want to learn more about recognizing prime and composite numbers? Check out this video.
Want more ways to think about prime and composite numbers? Check out this article.

Practice set 2: Identifying composite numbers

Problem 2A
Which of these numbers is composite?
29, 41, 47, 82, 89\large{29,\ 41,\ 47,\ 82,\ 89}
Choose 1 answer:
Choose 1 answer:

Want to try more problems like this? Check out this exercise.